linux-kernel - Re: [PATCH v4 2/9] serdev: Add an API to find the serdev controller associated with the devicetree node

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Message-ID: <2a44e967-ebae-4641-88d7-ccb4536ee3b7@kernel.org>
Date: Wed, 14 Jan 2026 15:01:51 +0100
From: Hans de Goede <hansg@...nel.org>
To: manivannan.sadhasivam@....qualcomm.com, Rob Herring <robh@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
 Nicolas Schier <nicolas.schier@...ux.dev>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Mark Pearson <mpearson-lenovo@...ebb.ca>,
 "Derek J. Clark" <derekjohn.clark@...il.com>,
 Manivannan Sadhasivam <mani@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Marcel Holtmann <marcel@...tmann.org>,
 Luiz Augusto von Dentz <luiz.dentz@...il.com>,
 Bartosz Golaszewski <brgl@...ev.pl>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Bartosz Golaszewski <brgl@...nel.org>
Cc: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kbuild@...r.kernel.org, platform-driver-x86@...r.kernel.org,
 linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, linux-bluetooth@...r.kernel.org,
 linux-pm@...r.kernel.org, Stephan Gerhold <stephan.gerhold@...aro.org>,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 linux-acpi@...r.kernel.org
Subject: Re: [PATCH v4 2/9] serdev: Add an API to find the serdev controller
 associated with the devicetree node

Hi Mani,

Thank you for your work in this.

On 12-Jan-26 17:26, Manivannan Sadhasivam via B4 Relay wrote:
> From: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> 
> Add of_find_serdev_controller_by_node() API to find the serdev controller
> device associated with the devicetree node.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> ---
>  drivers/tty/serdev/core.c | 16 ++++++++++++++++
>  include/linux/serdev.h    |  9 +++++++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
> index b33e708cb245..25382c2d63e6 100644
> --- a/drivers/tty/serdev/core.c
> +++ b/drivers/tty/serdev/core.c
> @@ -504,6 +504,22 @@ struct serdev_controller *serdev_controller_alloc(struct device *host,
>  }
>  EXPORT_SYMBOL_GPL(serdev_controller_alloc);
>  
> +/**
> + * of_find_serdev_controller_by_node() - Find the serdev controller associated
> + *					 with the devicetree node
> + * @node:	Devicetree node
> + *
> + * Return: Pointer to the serdev controller associated with the node. NULL if
> + * the controller is not found.
> + */
> +struct serdev_controller *of_find_serdev_controller_by_node(struct device_node *node)
> +{
> +	struct device *dev = bus_find_device_by_of_node(&serdev_bus_type, node);
> +
> +	return (dev && dev->type == &serdev_ctrl_type) ? to_serdev_controller(dev) : NULL;
> +}
> +EXPORT_SYMBOL_GPL(of_find_serdev_controller_by_node);
> +

This new of_find_serdev_controller_by_node() function needs:

#ifdef CONFIG_OF ... #endif

around it, to match the stubbing you are doing in serdev.h

>  static int of_serdev_register_devices(struct serdev_controller *ctrl)
>  {
>  	struct device_node *node;
> diff --git a/include/linux/serdev.h b/include/linux/serdev.h
> index ecde0ad3e248..db9bfaba0662 100644
> --- a/include/linux/serdev.h
> +++ b/include/linux/serdev.h
> @@ -333,4 +333,13 @@ static inline bool serdev_acpi_get_uart_resource(struct acpi_resource *ares,
>  }
>  #endif /* CONFIG_ACPI */
>  
> +#ifdef CONFIG_OF
> +struct serdev_controller *of_find_serdev_controller_by_node(struct device_node *node);
> +#else
> +struct serdev_controller *of_find_serdev_controller_by_node(struct device_node *node)
> +{
> +	return NULL;
> +}

stubs like this one should be static inline to avoid warnings like this one:

In file included from drivers/tty/serdev/core.c:21:
./include/linux/serdev.h:339:27: warning: no previous prototype for ‘of_find_serdev_controller_by_node’ [-Wmissing-prototypes]
  339 | struct serdev_controller *of_find_serdev_controller_by_node(struct device_node *node)
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Regards,

Hans